1. T cells in the immune system can be categorized into different types. What type of T cell directly kills infected body cells?

A. Helper T cells
B. Cytotoxic T cells
C. Regulatory T cells
D. Memory T cells

Correct answer: B

Rationale: Cytotoxic T cells directly kill infected body cells. These T cells recognize and destroy cells that are infected with viruses or other pathogens. They are crucial for eliminating threats within the body. Helper T cells, on the other hand, assist in coordinating the immune response by activating other immune cells. Regulatory T cells help maintain immune tolerance and prevent autoimmune reactions. Memory T cells are responsible for 'remembering' specific pathogens to mount a faster and stronger immune response upon re-exposure. Therefore, cytotoxic T cells are the correct answer as they directly target and kill infected cells.

2. Which element has the same number of protons and neutrons?

A. Carbon (C)
B. Oxygen (O)
C. Lithium (Li)
D. Helium (He)

Correct answer: D

Rationale: Helium (He) - He-4 has 2 protons and 2 neutrons, while the other options have differing numbers.

3. Osteoporosis is a condition leading to weakened bones and increased risk of fractures. Which hormone plays a key role in bone health and is often affected in osteoporosis?

A. Estrogen
B. Testosterone
C. Thyroid hormone
D. Insulin

Correct answer: A

Rationale: Estrogen plays a crucial role in bone health by promoting the activity of bone-forming cells and inhibiting bone breakdown. In women, estrogen levels decrease significantly during menopause, leading to a higher risk of osteoporosis. This hormone helps maintain bone density and strength, making it essential for preventing bone loss and fractures. Testosterone, while important for overall health, does not have as significant of an impact on bone health as estrogen does. Thyroid hormone and insulin also have roles in the body, but they are not as directly linked to bone health as estrogen. Therefore, the correct answer is A: Estrogen.

4. Electrons occupy specific energy levels around the nucleus, but not in fixed orbits. This concept is captured by the:

A. Bohr model
B. Quantum mechanical model
C. Lewis structure
D. Octet rule

Correct answer: B

Rationale: Quantum mechanical model. Unlike the Bohr model with its defined electron paths, the quantum mechanical model uses probability distributions to describe electron locations within energy levels.

5. What is the pH value of a neutral solution?

A. 0
B. 7
C. 14
D. -7

Correct answer:

Rationale: A neutral solution has a pH of 7. The pH scale ranges from 0 to 14, with 7 being neutral.

6. What is the periodic law?

A. The statement that the properties of the elements are a periodic function of their atomic numbers.
B. The statement that the elements can be arranged in a table in which elements with similar properties are grouped together
C. The statement that the elements can be arranged in a table in which the atomic number of an element is equal to the number of protons in its nucleus
D. The statement that the elements can be arranged in a table in which the atomic mass of an element is equal to the number of neutrons in its nucleus.

Correct answer: A

Rationale: The periodic law states that the properties of elements are a periodic function of their atomic numbers. This means that when elements are arranged in order of increasing atomic number, there is a periodic repetition of their properties. This forms the basis for the modern periodic table. Option B describes the periodic table itself, while options C and D do not accurately describe the periodic law.